Wrought aluminum alloys of the Al—Cu—Mn system have relatively high room temperature strength, good manufacturability for forming operation and high heat resistance (to 250-300° C.). The optimum copper content in these alloys is 5-7% (hereinafter, in wt. %) which is equal or slightly higher compared to its maximum solubility in the aluminum solid solution (Al). This copper content leads to the formation of the maximum quantity of secondary Al2Cu phase precipitates during aging. Furthermore, all these alloys contain manganese in an amount of up to 1% which provides for their heat resistance and up to 0.25% zirconium which noticeably increases the stability of the aluminum solid solution by raising the recrystallization onset temperature.
Known is, for example, the AA2219 aluminum base alloy (Hatch J. E. (ed.) Aluminum: Properties and Physical Metallurgy, ASM, Metals. Park, 1984  Kaufman G. J. Properties of Aluminum Alloys: Fatigue Data and Effects of Temperature, Product Form, and Process Variables, Materials Park, ASM International, 2008, 574 p.) which contains 5.8-6.3% Cu, 0.2-0.4% Mn, 0.02-0.10% Ti, 0.05-0.15% V and 0.1-0.25% Zr.
Wrought semifinished products fabricated from this alloy ingots have relatively good room temperature mechanical properties. The high heat resistance of the AA2219 alloy at temperatures of up to 250-300° C. is mainly accounted for by the presence of the Al20Cu2Mn3 phase fine particles the content of which is within 1.5 vol. %.
Disadvantages of the above alloy are as follows. Heating this alloy to above 300° C. greatly reduces its strength due to the coarsening of the main reinforcing phase Al2Cu. Moreover, the method of fabricating wrought semifinished products from ingots is quite complex and includes high temperature homogenizing anneal, forming operation, heating the semifinished products to above 500° C. for quenching, water quenching and aging which makes the final product expensive. As a result of the high temperature homogenizing anneal of the AA2219 alloy, the secondary Al20Cu2Mn3 phase particles which determine the high temperature structural strength of the alloy become more than 500 nm in size. The low corrosion resistance of the AA2219 alloy requires the use of various protective coatings, and the low electrical conductivity of the AA2219 alloy (within 30% IACS in the T6 state) limits its electrical engineering applications. The main origin of its low electrical conductivity is the high content of alloying additions in the aluminum solid solution, e.g. copper and manganese.
Known is a high temperature high strength aluminum alloy, semiconductor wire, air wire and fabrication method (EP 0 787 811 A1, publ, Aug. 6, 1997). According to said invention, the aluminum base alloy contains 0.28-0.8% Zr; 0.1-0.8% Mn; 0.1-0.4% Cu; 0.16-0.3% Si and other additives. The method of wire fabrication from that alloy includes producing an alloy at a temperature of at least 750+227·(Z−0.28)° C. (where Z is the zirconium concentration in the alloy, wt. %), cooling at a rate of at least 0.1 K/s, fabricating the first (cast) piece, heat treatment of said cast piece at 320-390° C. for 30-200 h and deforming.
Disadvantages of said invention include the insufficient electrical conductivity of the alloy (lower than 53% IACS) and long heat treatment (more than 30 hours). The invention does not disclose the fabrication of any other wrought semifinished products than wires (e.g. sheets) from that alloy. Another disadvantage of that material is the insufficient heat resistance due to the low content of Al20Cu2Mn3 phase fine particles which determine the high temperature structural strength of the alloy.
The closest counterpart of this invention is the heat resistant aluminum base alloy and wrought semifinished product fabrication method (RU 2446222, publ. Mar. 27, 2012). The alloy contains the following component percentages: 0.9-1.9% Cu; 1.0-1.8% Mn; 0.2-0.64% Zr; 0.01-0.12% Sc; 0.15-0.4% Fe and 0.05-0.15% Si. The zirconium and scandium additives provide for the good mechanical properties of that alloy compared to AA2219 not only at room temperature but also after long-term 300° C. heat treatment.
The method of fabricating wrought semifinished products according to said invention includes producing a melt at a temperature that is at least 50° C. above the liquidus temperature, producing a cast piece by solidifying the alloy, deforming said cast piece at a temperature of within 350° C., an intermediate 300-455° C. anneal of the wrought piece, room temperature deforming of the annealed piece and a 300-350° C. to obtain the wrought semifinished product.
Disadvantages of said invention include the significant degradation of its strength on heating to above 550° C. due to the drastic coarsening of Al3(Zr,Sc) phase fine particles. This hinders the application of that material for high temperature soldering at 560-600° C., and the high price of scandium makes final products too expensive and limits their applications. Another disadvantage of the alloy is the rapid decomposition of the aluminum solid solution with the precipitation of Al3(Zr,Sc) phase fine particles during cast piece deforming which reduces forming operation manufacturability.